Johnston Press Staff

Average speed cameras have been installed over 250 miles on British roads, in areas around the country. They are installed in sections on the M1 near Derbyshire, Leicestershire and Nottinghamshire, and on the M621 in Leeds.

Scottish Transport Minister Humza Yousaf also said there had been a “significant positive impact” after they were installed on the A90 between Dundee and Stonehaven.

So how do they work? And how do you avoid a fine?

Average speed cameras work by tracking the speed of your car between two points. So the old habit of slowing down to go past the camera and then speeding up afterwards will not fool it.

The cameras will record your number plate when you pass the first camera, then again at the second, and perform a quick calculation based on the current time to work out how long it took you to travel between the two points.

If the time it took you to travel is quicker than could be done at the speed limit, you’ll get a fine in the post.

So, for example, if the speed limit is 30mph and you drove at 35mph for 30 seconds, you’d need to drive at 25mph for 30 seconds to balance out your speeding.

Do the cameras work at night?

Yes. They are fitted with infrared night vision to ensure they work night and day, and in any weather.

Can the cameras run out of film?

No. Unlike some other speed cameras, average speed cameras are all digital. So they can issue an unlimited number of fines.

Can the cameras catch motorbikes?

Yes.

An average speed measuring system on on 23 June 2014. (PHILIPPE HUGUEN/AFP/Getty Images)

If a vehicle changes lanes will they avoid any fines?

No. The cameras take pictures of every lane and cross-compare them.

So changing lanes won’t save you, contrary to popular belief.

If I speed through multiple sets in the same of road stretch, will I be fined multiple times?

It’s not likely. Not every camera is paired to every other.

Your speed may be compared between the first and fourth camera of four in a row. Or the second and fourth. Or second and third. Any combination is possible.

On a separate section of the same road, you could get fined again. So it’s worth not risking the ticket.

If you are less than 10 per cent above the limit, will you get a ticket?

National Police Chiefs Council advice has suggested 10 per cent as a buffer, but this is only advisory and in reality many forces are far stricter, especially as cameras become more accurate.

In fact, according to the law you can legally be fined for being just 1mph over.

The best method to avoid a speeding ticket is, of course, not to speed.